1. Technical Field of the Invention
The present invention relates to novel cosmetic compositions for topical application, for the photoprotection of the skin and/or the hair against ultraviolet radiation (such compositions hereinafter simply designated "sunscreen," "sunscreen/cosmetic" or "photoprotective/sunscreen" compositions), and to the use of same for the cosmetic applications indicated above.
This invention more especially relates to the aforesaid sunscreen/cosmetic compositions imparting enhanced photoprotection, comprising, in a cosmetically acceptable vehicle, carrier or diluent which comprises a continuous aqueous phase, particularly an oil-in-water emulsion, immixture of (i) at least one conventional photoprotective agent that is a UV screen (whether of UV-A and/or UV-B), including one or more organic sunscreen compounds (UV absorbers) and/or one or more inorganic (nano)pigments based on metal oxides, preferably based on titanium dioxide, that function by physically blocking UV irradiation (UV reflectors and/or UV diffusers), and (ii) at least one judiciously selected particular polymer compatible therewith.
2. Description of the Prior Art
It is well known to this art that light radiation of wavelengths of from 280 nm to 400 nm promotes tanning of the human epidermis, and that irradiation of wavelengths of from 280 to 320 nm, i.e., UV-B irradiation, causes erythema and burning of the skin which can impair the development of a natural tan; hence, such UV-B radiation must thus be screened from the skin.
It is also known to this art that UV-A radiation, of wavelengths from 320 to 400 nm, which tans the skin, also adversely affects it, in particular in the event of sensitive skin or a skin which is continually exposed to solar radiation.
UV-A rays cause, in particular, a loss in the elasticity of the skin and the appearance of wrinkles, promoting a premature aging thereof. Such irradiation promotes triggering of the erythematous reaction or enhances this reaction in certain individuals, and may even be the source of phototoxic or photoallergic reactions. Thus, it is desirable to also screen out UV-A radiation.
A wide variety of cosmetic compositions intended for the photoprotection (UV-A and/or UV-B) of human skin are known to this art.
These photoprotective/sunscreen compositions are typically oil-in-water emulsions (namely, a cosmetically acceptable vehicle, carrier or diluent comprising an aqueous continuous dispersing phase and an oily discontinuous dispersed phase) which contains, in various concentrations, one or more standard lipophilic and/or hydrophilic organic sunscreen compounds capable of selectively absorbing harmful or deleterious UV radiation. These sunscreen compounds (and the amounts thereof) are selected as a function of the desired sun protection factor (the sun protection factor (SPF) being expressed mathematically by the ratio of the irradiation time required to attain the erythema-forming threshold with the UV screening agent to the time required to attain the erythema-forming threshold in the absence of UV screening agent).
The inorganic pigments and nanopigments, collectively (nano)pigments, based on metal oxides, especially based on titanium dioxide, are known active materials for solar protection (by "nanopigments" are intended particulates of pigments, the average size of the primary particles of which generally not exceeding 100 nm, and which preferably ranges from 5 nm to 100 nm, even more preferably from 10 nm to 50 nm.)
It too is known that these inorganic materials, whether or not in combination with conventional organic screening compounds absorbing UV-A and/or UV-B irradiation, impart to the sunscreen compositions comprised thereof a certain relatively limited inherent or additional photoprotective characteristic, by physically blocking the UV rays (reflection and/or diffusion).
To improve the essentially cosmetic properties of the sunscreen/cosmetic compositions, and notably of those described above, it is now usual to formulate therein so-called emulsifying polymers, among which the crosslinked copolymers of the acrylic acid/C.sub.10 -C.sub.30 alkyl acrylate type, such as those marketed under the trademarks "PEMULEN TR-1" and "CARBOPOL 1342" by Goodrich, are representative.
Nonetheless, one of the disadvantages presented by most of the sunscreen/cosmetic compositions which contain such polymers, whether they are based on organic sunscreen compounds or on (nano)pigments, or mixtures thereof, is that their sun protection factors on skin, especially very sensitive skins and/or those continually exposed to the sun, remain insufficient.
Thus, need continues to exist in this art to improve further the photoprotective properties of the known sunscreen compositions, while naturally preserving their good cosmetic properties.